Magnetic Resonance Imaging (MRI) is commonly used to view the internal organs of medical patients. To create an image, the patient is placed into very strong static and varying magnetic and radio frequency (RF) fields. For this reason, MRI is generally prohibited for patients with implanted ferromagnetic and/or electrically conductive objects, such as pacemakers, implantable defibrillators and nerve stimulators. Although it is feasible to minimize and even eliminate the use of ferromagnetic materials in implanted devices, these types of devices still require electrically conductive components that are affected by the fields produced by an MRI scanner.
U.S. Pat. No. 7,917,213, authored by the inventors of the present invention and incorporated herein by reference describes in detail the electrical and dimensional parameters of an MRI compatible lead body which minimizes the induced voltages and currents that can cause localized heating and/or distortion of an MRI image. This design requires that the diameter and pitch of the conductive coil within the lead body be closely controlled over its entire length.
Current methods of producing implantable lead bodies utilize various methods of polymer deposition such as spraying, dip coating, and extruding, however, these methods do not provide axial and diametric control of the conductive coil within the required tolerances and are thus unsuitable for producing MRI compatible lead bodies.
The invention as described and claimed herein details a process for manufacturing MRI compatible lead bodies which maintains close control of the helix pitch as well as the position of the coil in relation to the center line of the lead body, both of which relate to achieving the target RF performance.